1. Field of the Invention
The present invention relates to communication networks, and more specifically to a method and apparatus for supporting keep-alive messages of point-to-point sessions in aggregation devices (e.g., network access servers and home gateways).
2. Related Art
Point-to-point sessions (“PPP sessions”) are often set up between remote systems (e.g., personal computer systems at homes) and communication networks. A PPP session generally allows data transfer between a remote system and a termination device situated at the edge of a communication network. The termination device usually provides additional communication to enable a remote system (at one end of a session) to communicate with a target host as is also well known in the relevant arts. The communication between a host and a remote system forms the basis for several user applications.
Point-to-point protocol (PPP) described in request for comment (RFC) 1661, available from www.ietf.org, is a common protocol for establishing point-to-point sessions. As described in RFC 1661, communication networks may be implemented using transport protocols such as Internet Protocol, ATM and/or Frame Relay. As the host systems and remote systems are at either end of corresponding applications, the two systems are commonly referred to as end systems.
End systems send and receive data from aggregation devices, which are located at the edge of communication networks. The aggregation devices which are close to the remote systems may be referred to as network access servers (NAS) and the devices which are close to the host are referred to as home gateways. In general, an aggregation device serves as a common node in the path of several sessions, and interfaces with the corresponding (close) end systems.
An end system may send a keep-alive message typically to check the status of the end to end connection supporting a session. For example, in the case of extended period of inactivity on a session, an end system may wish to check whether the inactivity is due to outage in the underlying connection path or merely due to the inherent operation of applications using the session. If the keep alive message is not received back, the end system may release the session, thereby releasing resources such as session related queues and other memory entries in devices in the session path. Such release typically leads to more optimal use of the resources in networks.
In one prior system, an aggregation device forwards each received keep alive message to the other (“peer”) aggregation device at the edge of the communication network. The other aggregation device responds back indicating the status of the tunnel. The status information may be communicated to the end system originating the keep-alive message.
One problem with such a prior system is that a network may support many sessions, and the keep-alive data transfers may consume an undesirable amount of available bandwidth on the network. As a result, the prior art approach may be unacceptable at least in some environments. Accordingly, what is needed is a method and apparatus which allows the bandwidth on the network to be optimally used while potentially continuing support for the end systems in relation to keep alive messages.